The field of art to which this invention relates is medical devices, in particular, removable stent devices having bioabsorbable or biodegradable polymer coatings.
The use of stent medical devices, or other types of endoluminal mechanical support devices, to keep a duct, vessel or other body lumen open in the human body has developed into a primary therapy for lumen stenosis or obstruction. The use of stents in various surgical procedures has quickly become accepted as experience with stent devices accumulates, and the number of surgical procedures employing them increases as their advantages become more widely recognized. For example, it is known to use stents in body lumens in order to maintain open passageways such as the prostatic urethra, the esophagus, the biliary tract, intestines, and various coronary arteries and veins, as well as more remote cardiovascular vessels such as the femoral artery, etc. There are two types of stents that are presently utilized: permanent stents and temporary stents. A permanent stent is designed to be maintained in a body lumen for an indeterminate amount of time. Temporary stents are designed to be maintained in a body lumen for a limited period of time in order to maintain the patency of the body lumen, for example, after trauma to a lumen caused by a surgical procedure or an injury. Permanent stents are typically designed to provide long term support for damaged or traumatized wall tissues of the lumen. There are numerous conventional applications for permanent stents including cardiovascular, urological, gastrointestinal, and gynecological applications.
It is known that permanent stents, over time, become encapsulated and covered with endothelium tissues, for example, in cardiovascular applications. Similarly, permanent stents are known to become covered by epithelium, for example, in urethral applications. Temporary stents, on the other hand are designed to maintain the passageway of a lumen open for a specific, limited period of time, and preferably do not become incorporated into the walls of the lumen by tissue ingrowth or encapsulation. Temporary stents may advantageously be eliminated from body lumens after a predetermined, clinically appropriate period of time, for example, after the traumatized tissues of the lumen have healed and a stent is no longer needed to maintain the patency of the lumen. For example, temporary stents can be used as substitutes for in-dwelling catheters for applications in the treatment of prostatic obstruction or other urethral stricture diseases. Another indication for temporary stents in a body lumen is after energy ablation, such as laser or thermal ablation, or irradiation of prostatic tissue, in order to control post-operative acute urinary retention or other body fluid retention.
It is known in the art to make both permanent and temporary stents from various conventional, biocompatible metals. However, there are several disadvantages that may be associated with the use of metal stents. For example, it is known that the metal stents may become encrusted, encapsulated, epithelialized or ingrown with body tissue. The stents are known to migrate on occasion from their initial insertion location. Such stents are known to cause irritation to the surrounding tissues in a lumen. Also, since metals are typically much harder and stiffer than the surrounding tissues in a lumen, this may result in an anatomical or physiological mismatch, thereby damaging tissue or eliciting unwanted biologic responses. Although permanent metal stents are designed to be implanted for an indefinite period of time, it is sometimes necessary to remove permanent metal stents. For example, if there is a biological response-requiring surgical intervention, often the stent must be removed through a secondary procedure. If the metal stent is a temporary stent, it will also have to be removed after a clinically appropriate period of time. Regardless of whether the metal stent is categorized as permanent or temporary, if the stent has been encapsulated, epithelialized, etc., the surgical removal of the stent will resultingly cause undesirable pain and discomfort to the patient and possibly additional trauma to the lumen tissue. In addition to the pain and discomfort, the patient must be subjected to an additional time consuming and complicated surgical procedure with the attendant risks of surgery, in order to remove the metal stent.
Similar complications and problems, as in the case of metal stents, may well result when using permanent stents made from non-absorbable biocompatible polymer or polymer-composites although these materials may offer certain benefits such as reduction in stiffness.
It is known to use bioabsorbable and biodegradable materials for manufacturing temporary stents. The conventional bioabsorbable or bioresorbable materials from which such stents are made are selected to absorb or degrade over time, thereby eliminating the need for subsequent surgical procedures to remove the stent from the body lumen. In addition to the advantages attendant with not having to surgically remove such stents, it is known that bioabsorbable and biodegradable materials tend to have excellent biocompatibility characteristics, especially in comparison to most conventionally used biocompatible metals in certain sensitive patients. Another advantage of stents made from bioabsorbable and biodegradable materials is that the mechanical properties can be designed to substantially eliminate or reduce the stiffness and hardness that is often associated with metal stents, which can contribute to the propensity of a stent to damage a vessel or lumen.
However, there are disadvantages and limitations known to be associated with the use of bioabsorbable or biodegradable stents. The limitations arise from the characteristics of the materials from which such stents are made. One of the problems associated with the current stents is that the materials break down too quickly. This improper breakdown or degradation of a stent into large, rigid fragments in the interior of a lumen, such as the urethra, may cause obstruction to normal flow, such as voiding, thereby interfering with the primary purpose of the stent in providing lumen patency. Alternatively, they take a long time to breakdown and stay in the target lumen for a considerable period of time after their therapeutic use has been accomplished. There is thus a long-term risk associated with these materials to form stones when uretheral stents made from longer degrading biodegradable polymers.
Accordingly, there is a need in this art for novel, temporary stents, wherein the stents remain functional in a body lumen for the duration of a prescribed, clinically appropriate period of time to accomplish the appropriate therapeutical purpose, and, then soften and are removable as an elongated string-like member without producing fragments, which may cause irritation, obstruction, pain or discomfort to the patient, and without the need for a surgical procedure.
In a preferred embodiment of the present invention, the temporary stent readily passes out of the body, or is removed as, a limp, flexible string-like member, and irritation, obstruction, pain or discomfort to the patient is either eliminated, or if present, is minimal.
It is an object of the present invention to provide a stent for insertion into a body lumen which is manufactured from a flexible filament member, such as a suture, and then coated with a biodegradable or bioabsorbale polymer such that the member is formed into a relatively rigid stent, and when in the body, softens back into a flexible filament member which is easily passed or removed from the body lumen after a specific therapeutic period of time.
Therefore, an implantable stent is disclosed for use in body lumens, wherein such lumens exist as part of the natural anatomy or are made surgically. The stent is an elongate, hollow member having a helical or coiled structure, and in a preferred embodiment has a helical structure having a plurality of coils. The structure has a longitudinal axis and a longitudinal passage. The coils have a pitch. The structure is made from a flexible, limp filament or fiber, such as a surgical suture, having an exterior polymeric coating. The polymeric coating is a bioabsorbable or biodegradable polymer, or blend thereof. At body temperature, the coating is solid, and of sufficient thickness to effectively cause the flexible, limp member to be maintained in a substantially rigid, fixed state as a structure. The rate of degradation or absorption of the coating in vivo is sufficient to effectively soften or be removed from the outer surface of the filament within the desired therapeutic period. This effectively provides that as the coating degrades, softens or is absorbed in vivo, it loses its mechanical integrity. This allows the filament to revert to its natural, flexible limp state, causing the stent structure to effectively collapse, and the filament may be removed or eliminated from the lumen.
Upon in vivo exposure to body fluids, the progressively degrading and/or absorbing coating causes the stent to soften and collapse into a flexible filament that can readily pass out of the body lumen, either by manipulation or through natural expulsion with body fluids, thereby minimizing the possibility of causing obstruction, pain or discomfort.
Yet another aspect of the present invention is the above-described stent made from a fiber which is radio-opaque.
Yet another aspect of the present invention is a method of using the stents of the present invention in a surgical procedure to maintain the patency of a body lumen. A stent of the present invention is provided. The stent is an elongate, hollow member and in a preferred embodiment has a helical structure having a plurality of coils. The member has a longitudinal axis. The coils have a pitch. The structure is made from a flexible, limp filament or a fiber, having an outer surface and an exterior polymeric coating. The stent is inserted into a body lumen. The exposure to in vivo body fluids causes the exterior coating to absorb and/or degrade and soften, thereby causing the stent structure to collapse and return to a limp, flexible filament that can then be either eliminated by the passage of body fluids or manually removed.
These and other aspects of the present invention will become more apparent from the following description and examples, and accompanying drawings.